OpenVPN has the ability to choose different X509 field in case "CN" can
not be use used to be unique connected username since commit
935c62be9c0c8a256112df818bfb8470586a23b6 "Choose a different field in
X509 to be username".
Unfortunately it's not enough in case when client has multiple and
valid certificates from PKI for different devices (ex. laptop,
mobile, etc) with the same CN/UID.
Having --duplicate-cn as a workaround helps only partially: clients can
be connected, but it breaks coexistance with --ifconfig-pool-persist,
--client-config-dir and opens doors to DoS possibility since same client
device (with the same cert) being reconnected no more replaces previously
connected session, so it can exhaust server resources (ex. address pool)
and can prevent other clients to be connected.
With this patch, multiple X509 fields incl. "serialNumber" can be chosen
to be username with --x509-username-field parameters, they will be
concatened into the one username using '_' separator. As long as the
resulting username is unique, --duplicate-cn will not be required.
Default field is preserved as "CN".
Openssl backend is the only supported, since so far MbedTLS has no
--x509-username-field support at all.
v2: conform C99, man update, fix typos
v3: reuse buffer methods, drop delimiter define, use memcpy
v4: man update, change separator "_" to avoid path issues on windows
v5: mention collision possibility with "_" separator in man
capitalize hex serialNumber value
Signed-off-by: Vladislav Grishenko <themi...@yandex-team.ru>
---
doc/man-sections/tls-options.rst | 21 ++++++++++----
src/openvpn/init.c | 6 ++--
src/openvpn/options.c | 49 +++++++++++++++++---------------
src/openvpn/options.h | 4 +--
src/openvpn/ssl_common.h | 6 +++-
src/openvpn/ssl_verify.c | 49 +++++++++++++++++++++++++-------
src/openvpn/ssl_verify_openssl.c | 15 ++++++++++
7 files changed, 104 insertions(+), 46 deletions(-)
diff --git a/doc/man-sections/tls-options.rst b/doc/man-sections/tls-options.rst
index 8c2db7cd..5dd20013 100644
--- a/doc/man-sections/tls-options.rst
+++ b/doc/man-sections/tls-options.rst
@@ -632,20 +632,23 @@ certificates and keys: https://github.com/OpenVPN/easy-rsa
options can be defined to track multiple attributes.
--x509-username-field args
- Field in the X.509 certificate subject to be used as the username
- (default :code:`CN`).
+ Fields in the X.509 certificate subject to be used as the username
+ (default :code:`CN`). If multiple fields are specified their values
+ will be concatenated into the one username using :code:`_` symbol
+ as a separator.
Valid syntax:
::
- x509-username-field [ext:]fieldname
+ x509-username-field [ext:]fieldname [[ext:]fieldname...]
- Typically, this option is specified with **fieldname** as
+ Typically, this option is specified with **fieldname** arguments as
either of the following:
::
x509-username-field emailAddress
x509-username-field ext:subjectAltName
+ x509-username-field CN serialNumber
The first example uses the value of the :code:`emailAddress` attribute
in the certificate's Subject field as the username. The second example
@@ -653,16 +656,22 @@ certificates and keys: https://github.com/OpenVPN/easy-rsa
``fieldname`` :code:`subjectAltName` be searched for an rfc822Name
(email) field to be used as the username. In cases where there are
multiple email addresses in :code:`ext:fieldname`, the last occurrence
- is chosen.
+ is chosen. The last example uses the value of the :code:`CN` attribute
+ in the Subject field, combined with the :code:`_` separator and the
+ hexadecimal representation of the certificate's :code:`serialNumber`.
When this option is used, the ``--verify-x509-name`` option will match
against the chosen ``fieldname`` instead of the Common Name.
Only the :code:`subjectAltName` and :code:`issuerAltName` X.509
- extensions are supported.
+ extensions and :code:`serialNumber` X.509 attribute are supported.
**Please note:** This option has a feature which will convert an
all-lowercase ``fieldname`` to uppercase characters, e.g.,
:code:`ou` -> :code:`OU`. A mixed-case ``fieldname`` or one having the
:code:`ext:` prefix will be left as-is. This automatic upcasing feature is
deprecated and will be removed in a future release.
+
+ Non-compliant symbols are being replaced with the :code:`_` symbol, same as
+ the field separator, so concatenating multiple fields with such or :code:`_`
+ symbols can potentially lead to username collisions.
diff --git a/src/openvpn/init.c b/src/openvpn/init.c
index 31ecadcc..f87c11e7 100644
--- a/src/openvpn/init.c
+++ b/src/openvpn/init.c
@@ -2916,14 +2916,14 @@ do_init_crypto_tls(struct context *c, const unsigned
int flags)
to.crl_file_inline = options->crl_file_inline;
to.ssl_flags = options->ssl_flags;
to.ns_cert_type = options->ns_cert_type;
- memmove(to.remote_cert_ku, options->remote_cert_ku,
sizeof(to.remote_cert_ku));
+ memcpy(to.remote_cert_ku, options->remote_cert_ku,
sizeof(to.remote_cert_ku));
to.remote_cert_eku = options->remote_cert_eku;
to.verify_hash = options->verify_hash;
to.verify_hash_algo = options->verify_hash_algo;
#ifdef ENABLE_X509ALTUSERNAME
- to.x509_username_field = (char *) options->x509_username_field;
+ memcpy(to.x509_username_field, options->x509_username_field,
sizeof(to.x509_username_field));
#else
- to.x509_username_field = X509_USERNAME_FIELD_DEFAULT;
+ to.x509_username_field[0] = X509_USERNAME_FIELD_DEFAULT;
#endif
to.es = c->c2.es;
to.net_ctx = &c->net_ctx;
diff --git a/src/openvpn/options.c b/src/openvpn/options.c
index 658ca53f..772323df 100644
--- a/src/openvpn/options.c
+++ b/src/openvpn/options.c
@@ -876,7 +876,7 @@ init_options(struct options *o, const bool init_gc)
o->tls_cert_profile = NULL;
o->ecdh_curve = NULL;
#ifdef ENABLE_X509ALTUSERNAME
- o->x509_username_field = X509_USERNAME_FIELD_DEFAULT;
+ o->x509_username_field[0] = X509_USERNAME_FIELD_DEFAULT;
#endif
#ifdef ENABLE_PKCS11
o->pkcs11_pin_cache_period = -1;
@@ -8539,41 +8539,44 @@ add_option(struct options *options,
x509_track_add(&options->x509_track, p[1], msglevel, &options->gc);
}
#ifdef ENABLE_X509ALTUSERNAME
- else if (streq(p[0], "x509-username-field") && p[1] && !p[2])
+ else if (streq(p[0], "x509-username-field") && p[1])
{
- /* This option used to automatically upcase the fieldname passed as the
- * option argument, e.g., "ou" became "OU". Now, this "helpfulness" is
+ /* This option used to automatically upcase the fieldnames passed as
the
+ * option arguments, e.g., "ou" became "OU". Now, this "helpfulness" is
* fine-tuned by only upcasing Subject field attribute names which
consist
* of all lower-case characters. Mixed-case attributes such as
* "emailAddress" are left as-is. An option parameter having the "ext:"
* prefix for matching X.509v3 extended fields will also remain
unchanged.
*/
- char *s = p[1];
-
VERIFY_PERMISSION(OPT_P_GENERAL);
- if (strncmp("ext:", s, 4) != 0)
+ for (size_t j = 1; j < MAX_PARMS && p[j] != NULL; ++j)
{
- size_t i = 0;
- while (s[i] && !isupper(s[i]))
- {
- i++;
- }
- if (strlen(s) == i)
+ char *s = p[j];
+
+ if (strncmp("ext:", s, 4) != 0)
{
- while ((*s = toupper(*s)) != '\0')
+ size_t i = 0;
+ while (s[i] && !isupper(s[i]))
+ {
+ i++;
+ }
+ if (strlen(s) == i)
{
- s++;
+ while ((*s = toupper(*s)) != '\0')
+ {
+ s++;
+ }
+ msg(M_WARN, "DEPRECATED FEATURE: automatically upcased the
"
+ "--x509-username-field parameter to '%s'; please
update your"
+ "configuration", p[j]);
}
- msg(M_WARN, "DEPRECATED FEATURE: automatically upcased the "
- "--x509-username-field parameter to '%s'; please update
your"
- "configuration", p[1]);
}
+ else if (!x509_username_field_ext_supported(s+4))
+ {
+ msg(msglevel, "Unsupported x509-username-field extension: %s",
s);
+ }
+ options->x509_username_field[j-1] = p[j];
}
- else if (!x509_username_field_ext_supported(s+4))
- {
- msg(msglevel, "Unsupported x509-username-field extension: %s", s);
- }
- options->x509_username_field = p[1];
}
#endif /* ENABLE_X509ALTUSERNAME */
#ifdef ENABLE_PKCS11
diff --git a/src/openvpn/options.h b/src/openvpn/options.h
index 877e9396..e527d70e 100644
--- a/src/openvpn/options.h
+++ b/src/openvpn/options.h
@@ -584,8 +584,8 @@ struct options
int handshake_window;
#ifdef ENABLE_X509ALTUSERNAME
- /* Field used to be the username in X509 cert. */
- char *x509_username_field;
+ /* Field list used to be the username in X509 cert. */
+ char *x509_username_field[MAX_PARMS];
#endif
/* Old key allowed to live n seconds after new key goes active */
diff --git a/src/openvpn/ssl_common.h b/src/openvpn/ssl_common.h
index 96897e48..53f74cac 100644
--- a/src/openvpn/ssl_common.h
+++ b/src/openvpn/ssl_common.h
@@ -284,7 +284,11 @@ struct tls_options
const char *remote_cert_eku;
uint8_t *verify_hash;
hash_algo_type verify_hash_algo;
- char *x509_username_field;
+#ifdef ENABLE_X509ALTUSERNAME
+ char *x509_username_field[MAX_PARMS];
+#else
+ char *x509_username_field[2];
+#endif
/* allow openvpn config info to be
* passed over control channel */
diff --git a/src/openvpn/ssl_verify.c b/src/openvpn/ssl_verify.c
index 97ccb93b..76260967 100644
--- a/src/openvpn/ssl_verify.c
+++ b/src/openvpn/ssl_verify.c
@@ -645,7 +645,6 @@ verify_cert(struct tls_session *session,
openvpn_x509_cert_t *cert, int cert_dep
{
result_t ret = FAILURE;
char *subject = NULL;
- char common_name[TLS_USERNAME_LEN+1] = {0}; /* null-terminated */
const struct tls_options *opt;
struct gc_arena gc = gc_new();
@@ -668,19 +667,47 @@ verify_cert(struct tls_session *session,
openvpn_x509_cert_t *cert, int cert_dep
string_replace_leading(subject, '-', '_');
/* extract the username (default is CN) */
- if (SUCCESS != backend_x509_get_username(common_name, sizeof(common_name),
- opt->x509_username_field, cert))
+ struct buffer buf = alloc_buf_gc(256, &gc);
+ for (int i = 0; opt->x509_username_field[i] != NULL; i++)
{
- if (!cert_depth)
+ char username[TLS_USERNAME_LEN+1] = {0}; /* null-terminated */
+
+ if (SUCCESS != backend_x509_get_username(username, sizeof(username),
+ opt->x509_username_field[i],
cert))
{
- msg(D_TLS_ERRORS, "VERIFY ERROR: could not extract %s from X509 "
- "subject string ('%s') -- note that the username length is "
- "limited to %d characters",
- opt->x509_username_field,
- subject,
- TLS_USERNAME_LEN);
- goto cleanup;
+ if (!cert_depth)
+ {
+ msg(D_TLS_ERRORS, "VERIFY ERROR: could not extract %s from
X509 "
+ "subject string ('%s') -- note that the field length is "
+ "limited to %d characters",
+ opt->x509_username_field[i],
+ subject,
+ TLS_USERNAME_LEN);
+ goto cleanup;
+ }
+ break;
}
+ if (!buf_printf(&buf, i ? "_%s" : "%s", username))
+ {
+ if (!cert_depth)
+ {
+ msg(D_TLS_ERRORS, "VERIFY ERROR: could not append %s from X509
"
+ "certificate -- note that the username length is "
+ "limited to %d characters",
+ opt->x509_username_field[i],
+ buf.capacity - 1);
+ goto cleanup;
+ }
+ break;
+ }
+ }
+
+ char *common_name = BSTR(&buf);
+ if (!common_name)
+ {
+ msg(D_TLS_ERRORS, "VERIFY ERROR: depth=%d, could not extract X509 "
+ "username string from certificate", cert_depth);
+ goto cleanup;
}
/* enforce character class restrictions in common name */
diff --git a/src/openvpn/ssl_verify_openssl.c b/src/openvpn/ssl_verify_openssl.c
index 454efeec..34e1de01 100644
--- a/src/openvpn/ssl_verify_openssl.c
+++ b/src/openvpn/ssl_verify_openssl.c
@@ -269,6 +269,21 @@ backend_x509_get_username(char *common_name, int cn_len,
return FAILURE;
}
}
+ else if (strcmp(LN_serialNumber,x509_username_field) == 0)
+ {
+ ASN1_INTEGER *asn1_i = X509_get_serialNumber(peer_cert);
+ struct gc_arena gc = gc_new();
+ char *serial = format_hex_ex(asn1_i->data, asn1_i->length,
+ 0, 1 | FHE_CAPS, NULL, &gc);
+
+ if (!serial || cn_len <= strlen(serial)+2)
+ {
+ gc_free(&gc);
+ return FAILURE;
+ }
+ openvpn_snprintf(common_name, cn_len, "0x%s", serial);
+ gc_free(&gc);
+ }
else
#endif
if (FAILURE == extract_x509_field_ssl(X509_get_subject_name(peer_cert),
--
2.17.1
_______________________________________________
Openvpn-devel mailing list
Openvpn-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/openvpn-devel
